An organism's immune system in one aspect serves to protect it from infection, generally through an innate immune system and an adaptive immune system. On a simple level, organisms rely on physical barriers to prevent pathogens such as bacteria and viruses from entering them. In the event that a pathogen breaches these barriers, the innate immune system is at the ready to provide an immediate, but non-specific response. On a more complex level, when pathogens evade the innate response, some animals are equipped with a third element, the adaptive immune system.
Several types of barriers protect organisms from infection, including mechanical, chemical and biological barriers. The skin of an animal is an example of a biological barrier on the front line of exposure environmental agents an organism might encounter. Composite skin replacement using cultured autologous keratinocytes on acellular allogenic dermis has been used as a skin substitute with promise for burn victim patients (Robert L. Sheridan et al. Burns 2000. 27: 421-424).
Phagocytosis is an important feature of cellular innate immunity. Cells classified as phagocytes are able to engulf, or consume, agents, pathogens or particles. Phagocytes routinely patrol the animal body, e.g., in the skin, seeking out pathogens.
Dendritic cells (DC) are phagocytes found associated with tissues of an animal exposed to the environment. Dendritic cells can be found, for example, in the skin, cornea, nose, lungs, gastrointestinal tract and genitourinary tract. Dendritic cells are known as potent antigen-presenting cells involved in the induction of T cell-mediated immune responses. One important dendritic cell type is Langerhans cells. In recent years serum-free, closed culture systems for establishing and maintaining dendritic cells have been developed (Christina M. Celluzzi and Craig Welbon. 2003. Journal of Hematotherapy & Stem Cell Research., 12(5): 575-585).
Hypersensitivity is a type of immune response causing damage to an animal's own tissues. (Ghaffar, Abdul (2006). Immunology—Chapter Seventeen: Hypersensitivity Reactions. Microbiology and Immunology On-Line Textbook. USC School of Medicine; available at http://pathmicro.med.sc.edu/ghaffar/hyper00.htm; last visited Jan. 10, 2008) Hypersensitivity reactions are divided into four classes referred to as Type I-IV. (supra) Type I hypersensitivity involves an immediate or anaphylactic reaction, often associated with allergy and is mediated by IgE released from mast cells and basophils. (supra) Type II hypersensitivity or antibody-dependent (or cytotoxic) hypersensitivity is mediated by IgG and IgM antibodies. (supra) Type III hypersensitivity reactions can be triggered by immune complexes (including aggregations of antigens, complement proteins, and IgG and IgM antibodies) deposited in various tissues. (supra) Type IV hypersensitivity is referred to as cell-mediated or delayed type hypersensitivity and is involved in many autoimmune and infectious diseases, but may also involve contact dermatitis (e.g., poison ivy). (supra) Hypersensitivity reactions are mediated by, e.g., T cells, monocytes, and phagocytes (including dendritic cells and macrophages).
Understanding the interplay of environmental agents the immune system and hypersensitivity of an organism is both medically and commercially relevant.